The invention is in the field of solid state high-power lasers. In. most solid-state lasers, the lasing material is fabricated in the shape of round cylindrical rods. Lasers based on such rods provide a simple and low-cost means for obtaining laser output at low power levels. However, at high power levels, such rods exhibit serious limitations because of thermal lensing and thermal birefringence. Mild thermal lensing at a given power level can be corrected by using a compensating lens in the cavity. A more perfect and dynamic aberration correction has been achieved by using the technique of optical phase conjugation, usually based on stimulated scattering. Thermal birefringence of laser rods, however, remains a major problem. In round rods, the birefringence varies quadratically with radius and total compensation for it is very difficult. This imposes a limitation when a large volume of gain medium is needed. Round rods are, therefore, basically upward scalable only along one dimension, namely, length. Several years ago, General Electric Corporation made a major stride in overcoming thermal limitations of rod lasers by introducing the slab laser geometry with a zigzag beam path. The gain medium is fabricated in the form of a rectangular cross-section slab with relatively large parallel surfaces or faces parallel to the slab length. The laser beam is introduced into the slab through an end face cut at Brewster's angle. The beam then propagates through the slab in a zigzag path while undergoing total internal reflection at the large slab faces. Since the slab is rectangular and is pumped through and cooled from the large faces, the temperature gradient is one dimensional and the birefringence is X--Y type. There is no beam depolarization for a laser beam polarized for Brewster's angle. This contrasts sharply with the beam depolarization because of radial birefringence of a round rod. The zigzag path through the slab is effective in averaging out potential wavefront distortions caused by thermal lensing effects. Also, unlike round rods, the slab geometry allows scaling along two different dimensions, namely, the width and length. An increase in the width dimension of the slab can be made without increasing the distance between the hottest middle part and the cooled surfaces. In spite of its many attractive advantages, the GE zigzag slab laser suffers from several disadvantages. These disadvantages can be listed as follows: (1) Incomplete energy extraction because the zigzaging beam does not fill the active slab volume, (2) beam wander because of thermally induced slab bending, (3) sealing difficulties since the zigzaging laser beam directly strikes the large faces where the coolant seals are made, (4) the large slab faces must be kept optically clean, (5) the cost and difficulty of polishing large slab faces to exacting optical tolerances. The present invention overcomes those disadvantages by operating in a hybrid manner, i.e., it combines the best features of round rod and slab technologies.